AT A GLANCE
- Common Name: Antarctic Krill
- Scientific Name: Euphausia superba
- Category: Invertebrates
- Subcategory: Crustaceans
- Range: Circumpolar throughout the Southern Ocean surrounding Antarctica, south of the Antarctic Convergence
- Habitat Type: Pelagic open ocean, seasonal sea ice margins, and beneath drifting pack ice from surface waters down to depths of 1,000 meters
- IUCN Red List Status: Least Concern
- Lifespan: 5 to 7 years (exceptional for a small planktonic crustacean)
- Diet: Planktivorous/Herbivorous (primarily microalgae and phytoplankton, especially ice diatoms grazed off the underside of pack ice, alongside tintinnids and copepods)
- Average Size/Weight: Total length 5 to 6.5 cm; weight 1 to 2 g
- Key Defining Feature: Translucent, pinkish-amber shrimp-like crustacean with colossal black compound eyes, specialized feather-like phytoplankton-filtering legs, and brilliant blue bioluminescent photophores
Overview
Antarctic Krill (Euphausia superba) is arguably the single most ecologically critical animal species on planet Earth. Belonging to the crustacean order Euphausiacea, this modest-looking, translucent, shrimp-like invertebrate forms the foundational keystone of the entire Antarctic marine ecosystem. With an estimated total living biomass exceeding 400 to 500 million metric tons—outweighing all human beings on the planet combined—it transforms the vast microscopic energy of polar diatoms into living protein, sustaining the ocean’s greatest baleen whales, seals, penguins, and seabirds.
Biology and Physical Characteristics
Euphausia superba has a sleek, streamlined, laterally compressed body encased in a delicate, glassy chitinous exoskeleton of pale pinkish-amber or reddish-yellow with bright green digestive organs visible through its translucent shell. It possesses huge, spherical black compound eyes optimized for low-light polar conditions. Its six pairs of thoracic legs (pereiopods) are adorned with dense, comb-like setae that interlock to form an exquisite, high-precision ‘feeding basket’ capable of filtering microscopic unicellular diatoms out of seawater. Along its underside lie multiple specialized photophores—biological flashlights that emit an intense, glowing blue-green bioluminescent light, aiding in school cohesion and counterillumination camouflage.
Behavior and Ecology
Antarctic Krill are intensely social, swarming in immense schools that stretch for kilometers and contain up to 10,000 to 30,000 individuals per cubic meter of ocean, staining the sea surface vivid pink and red. In winter, when polar darkness descends and phytoplankton vanishes from the water column, krill migrate beneath drifting sea ice, turning upside down to scrape nutritious winter diatoms off the under-ice surface like lawnmowers. If starved, they perform an astonishing biological feat: they molt backwards, shrinking in body size and consuming their own body proteins to survive the dark polar winter.
Conservation and Human Impact
Antarctic Krill is evaluated as Least Concern by the IUCN Red List due to its colossal global biomass. However, it faces serious emerging challenges from accelerated Antarctic sea ice decline driven by global climate change, ocean acidification, and expanding industrial fisheries harvesting krill for omega-3 oils and aquaculture feed. Commercial catches are internationally regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).
Interesting Factoid
Antarctic Krill have the largest collective biomass of any wild animal species on Earth—weighing more than all the humans on the planet combined—and when food is scarce in winter, they can literally molt backwards to shrink their body size.